You can check if a PO file is valid with the following command:

        msgfmt -c -o /dev/null <po file>
      

The following errors were found in smartdns 's PO files:

gettext: package/luci-compat/files/luci/i18n/smartdns.zh-cn.po:659: end-of-line within string
package/luci-compat/files/luci/i18n/smartdns.zh-cn.po:811: duplicate message definition...
package/luci-compat/files/luci/i18n/smartdns.zh-cn.po:159: ...this is the location of the first definition
msgfmt: found 2 fatal errors
gettext: package/luci/files/luci/i18n/smartdns.zh-cn.po:668: end-of-line within string
package/luci/files/luci/i18n/smartdns.zh-cn.po:817: duplicate message definition...
package/luci/files/luci/i18n/smartdns.zh-cn.po:162: ...this is the location of the first definition
msgfmt: found 2 fatal errors
      

Please ask the translator (identified by the Last-Translator field in the PO file), the language team (identified by the Language-Team field) or debian-i18n for a fix.